The exhaust gas handling devices involved in the invention are, for example, silencers, but particularly emission control devices such as catalysts and Diesel particle filters.
Housed in such devices are inserts highly sensitive to radial pressure, these mainly involving hitherto ceramic substrates wrapped in an elastic compensating element (e.g. in the form of a matting). These inserts are, when possible, held in place both axially and laterally simply by being radially clamped in place whereby the clamping effect needs to be sufficient so that the insert is not shifted out of place relative to the outer housing axially due to the gas pressure and also due to vibrations in vehicle operation. On the other hand, the radial pressure must not be so high that the insert becomes ruined, particularly as regards ruining the substrate of the catalyst or Diesel particle filter sensitive to pressure loading. In addition to this, there is a need to engineer inserts with a reduced mass so that they attain the required temperature quicker in vehicle operation. Such substrates are structured for example in the form of a corrugated board type basic structure coated with a catalytic material.
Hitherto, the insert was inserted and clamped in place in the outer housing, i.e. canned, by wrapping the sheet metal jacket about the insert into a tube with or without subsequent calibrating or closing of shells. But when the force is applied excessively the insert, in other words the substrate of catalysts can be ruined.
One major difficulty in fabricating emission control devices is that the elastic compensating element disposed between the substrate and the outer housing is typically provided as support matting ensuring a permanently biased pressure compensation. The drawback of this support matting is, however, that after it is compressed it is subject to a certain settling (relaxation) resulting in the pressure transmitted thereby to the substrate being reduced. The rebound or spring-back of the outer housing after insertion and clamping in place also results in the pressure initially applied to the substrate and thus the applied clamping force being diminished. In addition to this, the pressure holding the support matting in place in operation deteriorates (for instance due to aging) resulting in the initial pressure needing to be increased even more to ensure the substrate is reliably clamped in place in the outer housing later, stressing the individual substrates to the limit of their stability.